PARIS, France—In patients undergoing percutaneous coronary intervention (PCI) who experience stent thrombosis, stent fracture and strut malapposition are common   regardless of stent type, according to late-breaking findings presented Thursday, May 27 at EuroPCR 2010. However, in patients with very late stent thrombosis, the incidence of incomplete stent apposition is 3 times higher with drug-eluting stents (DES) than with bare-metal stents (BMS).

For the Nordic IVUS study, researchers led by Petteri Kosonen, MD, of Tempere University Hospital (Tampere, Finland), used IVUS to analyze 124 Academic Research Consortium-defined stent thrombosis cases documented in the Nordic Registry from October 2007 to December 2009, assessing rates of fracture and incomplete stent apposition in patients with DES and BMS.

Stratified by the time of occurrence, the majority of the stent thrombosis cases occurred in the very late period in both the BMS and DES groups, with significantly more occurring after DES implantation during that time frame (table 1).

Table 1. Timing of Stent Thrombosis

^a P = 0.04

There were no significant differences between paclitaxel-eluting (PES) and sirolimus-eluting stents (SES) in terms of stent thrombosis rates at any particular time period.

Of the 124 stent thrombosis cases, 24 were stent fractures (19%), consisting of 6 partial fractures and 18 total fractures. Incidence rates were similar between DES and BMS (table 2).

Table 2. Timing of Stent Fractures

Again, there were no significant differences between PES and SES.

Incomplete stent apposition was found in more than a quarter of all BMS cases of stent thrombosis and in 43% of DES cases, and DES patients had a rate threefold higher than BMS patients during the very late period (table 3).

Table 3. Timing of Incomplete Stent Apposition

^a P = 0.02

In addition, there were more cases of incomplete stent apposition with SES (58%) compared with PES (32%; P = 0.02).

Dr. Kosonen and colleagues also found that the sum of the areas of malapposition in stent thrombosis cases occurring after 1 year was greater in DES patients than in BMS patients (2.97 ± 9.60 mm² vs. 0.19 ± 8.61 mm²; P = 0.01). This was also true for the total area of malapposition in stent thromboses occurring in DES patients before (0.98 ± 2.32 mm²) vs. after (2.97 ± 9.60 mm²; P = 0.013) 1 year, and after 1 year in SES (4.05 ± 12.0 mm²) vs. PES (2.06 ± 7.34 mm²; P = 0.06) patients, though the difference was not significant for the last comparison.

Cause of Late Malapposition Unknown

Dr. Kosonen cautioned that it is unknown as to whether the observed late malapposition is acquired or persistent since IVUS was not used when the stents were implanted. Nevertheless, “this awakens the question that in sirolimus stents, there might be more acquired late malapposition than in paclitaxel stents, but we can’t say for sure,” he said.

Overall, “we can conclude that stent fracture and stent strut malapposition are both common findings in stent thrombosis, both in BMS and DES patients,” Dr. Kosonen said. “Very late stent thrombosis was the most common presentation of stent thrombosis in both the BMS and DES groups. Stent fractures were quite common in both BMS and DES patients. There were high rates of incomplete stent apposition and large areas of malapposition observed in sirolimus-eluting stents.”

Session co-chair Laura Mauri, MD, MSc, of Brigham and Women’s Hospital (Boston, MA), asked Dr. Kosonen to explain the unusually high rates of very late stent thrombosis found in the Nordic IVUS study. “Normally, we think the risk is greater closer to the time of the procedure,” she said.

Dr. Kosonen explained that this may have resulted from selection bias, since the investigators chose only those patients in whom they were able to perform IVUS analysis.

“So this doesn’t represent all the cases of stent thrombosis?” Dr. Mauri asked. “Is that the simple answer?” To which Dr. Kosonen replied, “Yes.”

Additional analyses Dr. Kosonen hopes to perform in the Nordic IVUS cohort include vessel segment remodeling, the different types of BMS used, and the duration of dual antiplatelet therapy.

Study Details

Baseline characteristics were well matched between the DES (n = 87) and BMS (n = 37) groups, with the exception of diabetes, which was more prevalent in BMS patients (35% vs. 16%; P = 0.05). Procedural characteristics were also similar except for stent length, which was increased in DES patients (24.4 ± 9.7 mm vs. 19.3 ± 8.8 mm; P = 0.006).

Disclosures:

• Dr. Kosonen reports serving as a proctor for Edwards Lifesciences.
• Dr. Mauri reports no relevant conflicts of interest.

Related Stories:

• IVUS Offers Insights into Very Late Stent Thrombosis with DES, BMS
• Incomplete Apposition Implicated in Stent Thrombosis
• Elevated CRP Predicts Stent Thrombosis, Death, MI in DES Patients